In fleece manufacturing, the uniform supply of material is the prerequisite for high fleece uniformity. To feed the carding machines, so-called flock feeders are utilized that usually work according to the double shaft principle (DE 44 34 251). A fan blows the fiber material prepared by the mixing and opening equipment via a distribution line in the large upper shaft (the so-called material reserve shaft of the flock feeder) in whose lower end the fiber material is grabbed by a feeding roller and fed into an opening roller. For secure guidance, spring-mounted individual segments of a collecting trough clamp the fiber material against the feeding roller and these individual segments adjust themselves automatically according to the respective fiber mass. The fiber mass that is presented to the opening roller in this way is then opened by the opening roller and transported to the lower shaft, the actual feeding shaft for the carding machines. This is generally supported by an air current. A feeding roller that works together with spring-loaded, segmented troughs that sample the strength of the material and regulate accordingly has been placed in the lower end of the feeding shaft. Since the quantity throughput of the fiber material depends on the density of the material, the filling level is maintained as constant as possible in the feeding shaft and an air current brings about a uniform compression.
Several devices have been known for improving the compression air current at the exit of the feeding shaft, such as the one described in EP 0 929 704. However, that invention has the problem of once again carrying the compression air current away from the feeding shaft and separating it from the fiber material, and of also maintaining a uniform compression over the entire width of the feeding shaft. It is especially when the fleece machine is working very fast (when more than 1,000 kg/h of material must be fed into it) that the known equipment is incapable of equalizing the respective fluctuations without changing the filling level significantly, both in the reserve shaft and in the feeding shaft, which leads to uneven density in the fiber material and therefore has a negative effect on the uniformity of the fleece.
To achieve a continuous flow of material for the current demand of the fleece carding machine, other inventions have placed a dosing opener before the flock feeder so the latter can be uncoupled from the mixing and opening equipment. Since experience has shown that this uncoupling depends on bale loading and opening, the placing of a dosing opener before the flock feeder greatly improves operational safety (see Trültzschler brochure “Technologie Scanfeed TF Beschickung Dosieröffner FD-S” [The Technology of Scanfeeding TF Loading of the Dosing Opener FD-S]). This dosing opener consists of a large-volume filling shaft into which the fiber material coming from the mixing and opening equipment is blown. Photoelectric barriers control the filling level and the respective demand of material to request it from the mixing and opening equipment. This large dosing opener is not suitable for large throughput quantities of fiber material, however, because the fluctuation of material that occurs in the tall, space-saving mixing and opening equipment placed before it causes large height differences that lead to uneven density in the fiber material. The compression air current foreseen to compensate for the fluctuations in height is incapable of satisfactorily compensating for the fluctuations in height and therefore in density.